AIR MOTOR WITH MEANS TO PREVENT FREEZING

Abstract: An air motor of the reciprocating piston type has a piston (14) connected to a piston rod (13). The compressed air flow to the opposite sides of the piston is controlled by a control valve member (16) which is coupled by an actuating mechanism to the piston rod so that air is supplied to the opposite ends in turn of the cylinder (10) which contains the piston. The air is exhausted from the opposite ends of the cylinder through respective exhaust control valves each having a diaphragm (32). The exhaust control valves control the air flow into exhaust conduits (31, 35) which are constructed so that the expansion of the air takes place in portions of the conduits which are removed from the exhaust control valves thereby to minimise the risk of ice formation in the exhaust control valves.

Description: AIR MOTOR WITH MEANS TO PREVENT FREEZING This invention relates to an air motor of the kind comprising a cylinder, a piston movable within the cylinder, a piston rod coupled to the piston and extending from the cylinder, a control valve which controls the admission of compressed air to the opposite ends of the cylinder in turn, an actuating mechanism for the valve, said actuating mechanism acting to alter the setting of the control valve whereby as the piston attains a predetermined position as it approaches one end of the cylinder, the control valve will operate to admit compressed air to the one end of the cylinder to achieve reverse motion of the piston and vice versa, and means for allowing air to exhaust from the ends of the cylinder in turn. Such motors are well known in the art for driving reciprocating pumps, in particular pumps which deliver paint to a supply manifold. In known air motors the aforesaid control valve also acts to control the escape of the exhaust air from the ends of the cylinder. As the exhaust air flows through the valve expansion of the air takes place and as a result the temperature of the air is reduced. The temperature of the air can fall to the extent that moisture in the air freezes and the ice formed can hinder the operation of the control valve and also cause a reduction in the effective cross sectional area of the various passages which convey the exhaust air thereby resulting in a reduction in the operating speed of the motor. The reduction in speed results in a reduced pressure in the aforesaid supply manifold which is unacceptable. Moreover, if the operation of the valve is hindered the return stroke of the piston may be delayed leading to unacceptable fluctuation in the pressure in the manifold. It is known to heat the compressed air which is supplied to the motor but this requires a substantial amount of thermal energy. The object of the present invention is to provide an air motor of the kind specified in a simple and convenient form. According to the invention an air motor of the kind specified comprises a pair of exhaust conduits communicating with the opposite ends of the cylinder respectively, a pair of exhaust control valves for controlling the flow of air through said conduits respectively, said exhaust control valves being responsive to the setting of said first mentioned control valve, the exhaust conduits being constructed so that as the exhaust air flows therethrough a substantial proportion of the air expansion takes place in a portion of the conduit removed from the exhaust control valve. An example of an air motor in accordance with the invention will now be described with reference to the accompanying drawings in which:- Figure 1 is a sectional side elevation of the motor, Figure 2 is a plan view of the motor shown in Figure 1 with the cover removed, Figure 3 is an inverted plan view of the motor shown in Figure 1 , and Figure 4 is a view to an enlarged scale showing two of the valves of the motor seen in Figure 1. The drawings illustrate an air motor for actuating a double acting piston pump which is intended to supply paint under pressure to a paint manifold which conveys the paint to a plurality of spray guns. The air motor comprises a hollow cylinder 10 which is sandwiched between upper and lower end walls 1 1 , 12, these components being secured together by tie bolts. The lower end wall 12 is adapted to be secured to a mounting structure which also carries the pump and conveniently the motor is mounted above the pump. In the lower end wall there is provided a central aperture through which extends a hollow piston rod 13 which within the cylinder is secured to a piston 14. The usual seals are provided for the piston rod and the lower end thereof is adapted to be connected to the actuating member of the pump. Mounted centrally on the upper end wall 1 1 is a control valve housing 15 in which is formed a valve chamber which houses a control valve in the form of a slide valve member 16. There is also mounted on the upper end wall a further valve housing 28 to be described. The valve member 16 by reason of a spring loaded detent mechanism (not shown) has an upper stable position in which it is shown in the drawing, and a lower stable position. The slide valve member 16 is movable between these positions by an actuating mechanism in the form of an actuating rod 17 which extends downwardly into the piston rod 13. A reduced portion of the actuating rod carries upper and lower abutment collars 18, 19 which are held in spaced relationship by a compression spring. The upper abutment collar 18 is engagable with a collar 20 secured within the piston rod and the lower abutment collar 19 is engagable with a step 21 defined in the piston rod. The operation of the actuating mechanism is such that with the valve member 16 in its upper position, air is supplied to the upper portion of the cylinder to move the piston downwardly. As the piston approaches the lower end wall the collar 20 will engage with the upper abutment collar 18 and with continued movement of the piston the valve member 16 will move to its lower stable position so that air is supplied to the lower portion of the cylinder. The piston as a result moves upwardly and the process is repeated when the lower abutment collar 19 is engaged by the step 21 on the piston rod. Air under pressure from an external source is conveyed to a central port 22 in the valve housing 15. Conveniently the air is conveyed by an external pipe 23 which extends alongside the cylinder to an air inlet union 24 carried by the lower end wall 12. In its upper stable state the slide valve member connects the central port 22 with an upper port 25 and in its lower stable position the central port is connected to a lower port 26. The further valve housing 28 defines in conjunction with an insert 40 a valve chamber which contains a diaphragm 32 formed from synthetic resin material. The insert 40 has a circumferential groove 41 which by way of a transfer port 30 communicates with the upper portion of the cylinder. The insert 40 is provided with a central opening through which extends an exhaust conduit in the form of an exhaust pipe 31. The pipe 31 at its inner end is engageable by the diaphragm 32. Surrounding the inner end portion of the exhaust pipe is an annular recess 43 which is formed in the insert and the recess communicates with the circumferential groove by way of a plurality of blind drillings 43 which are formed in the inner end face of the insert, the drillings being formed before machining of the groove and recess. The effect of the drillings and the recess is to produce a discontinuous support surface for the outer portion of the diaphragm. The adjacent end wall of the further valve housing is recessed to allow for movement of the diaphragm away from the end of the pipe 31. A passage 29 formed in the further valve housing 28 connects the port 25 with the valve chamber, the entrance to the passage being enlarged to accommodate of a support insert 32A which is provided with a plurality of through apertures. When the slide valve member is in its upper stable position as shown, air under pressure entering the valve chamber through the passage 29 urges the diaphragm into engagement with the end of the pipe 31 and air flows around the periphery of the diaphragm into the groove 41 and then through the transfer port 30 into the cylinder. When the position of the slide valve is changed the pressure in the passage 29 suddenly falls and the diaphragm is lifted from the end of the exhaust pipe and moves into engagement with the support insert. Air can now escape from the cylinder as the piston moves upwardly and flows through the transfer port 30 into the groove 41 and then into the recess 42 and into the end of the exhaust pipe. The engagement of the diaphragm with the support insert prevents air flowing through the passage 29, the insert preventing extrusion of the diaphragm into the passage. A similar valve 33 is mounted on the lower end plate 12, this valve being connected to the lower port 26 of the slide valve by way of an external pipe 34. The valve 33 is provided with an exhaust pipe 35 and the two exhaust pipes are connected to an exhaust manifold 36 which leads to atmosphere through a silencer (not shown). The valves operate very quickly in response to the change in position of the slide valve member 16 so that the pressure fluctuation in the paint manifold is minimised. The upper exhaust pipe 31 extends through a bell shaped cover 37 which extends downwardly to adjacent the lower end plate 12. The cover may have an internal coating of a sound deadening medium. The two exhaust pipes 31 and 35 are machined from solid material and for substantially half their length define a passage or as shown, a pair of passages 37 of reduced cross sectional area as compared with the remaining portion 38 of the passage. The passages 37 extend from the end of the pipe within the valve chamber and the reduced cross section of the passages ensure that the expansion of the air as it leaves the cylinder, tends to take place in the portion 38 of the passage. This of course is remote from the associated valve housing and outside the cover 37. The expansion of the air produces the cooling effect mentioned but the risk of ice formation within the passage 38 is reduced by the provision of integral fins 39 on the exhaust pipe. The fins assist heat exchange between the atmosphere and the wall of the pipe so that in use the risk of ice formation on the inner wall of the exhaust pipe is minimised. The risk of restriction to the flow of exhaust air is therefore minimised. Moreover, the risk of ice formation within the exhaust control valve is minimised by ensuring that so far as possible, the air expands within the exhaust pipe. Furthermore, since the main control valve controls only the admission of air to the cylinders there is no risk of ice formation within the control valve. The construction described has significant advantages over the known constructions however, in particularly severe operating conditions there may be some ice formation in the exhaust control valves. The formation of ice can be minimised by introducing air into the valve chamber. This air can be obtained from the supply and may or may not be heated. It will be understood that the supply of such air is to be avoided if possible since it represents an energy loss. In the known constructions the main valve deals with the admission of air to the opposite ends of the cylinder and also the exhaust of air therefrom. In the known constructions the air is exhausted into the space within the cover and is a source of considerable noise. Moreover, since the air contains fine droplets of oil in order to provide for lubrication of the various parts, the oil is deposited in the vicinity of the valve and tends to be carried out and deposited on the floor around the motor and pump. With the proposed arrangement the exhaust air is conveyed away and there is a considerable reduction in the noise generated and furthermore there is no deposition of oil in the vicinity of the motor.

Claims: CLAIMS 1. An air motor comprising a cylinder, a piston movable within the cylinder, a piston rod coupled to the piston and extending from the cylinder, a control valve which controls the admission of compressed air to the opposite ends of the cylinder in turn, an actuating mechanism for the valve, said actuating mechanism acting to alter the setting of the control valve whereby as the piston attains a predetermined position as it approaches one end of the cylinder, the control valve will operate to admit compressed air to the one end of the cylinder to achieve reverse motion of the piston and vice versa, a pair of exhaust conduits communicating with the opposite ends of the cylinder, a pair of exhaust control valves for controlling the flow of air through said exhaust conduits respectively, said exhaust control valves being responsive to the setting of said first mentioned control valve, the exhaust conduits being constructed so that as the exhaust air flows therethrough a substantial proportion of the air expansion takes place in a part of the conduit removed from the exhaust control valve. 2. An air motor according to Claim 1 in which each exhaust conduit has an initial portion through which the exhaust air flows as it leaves the respective exhaust control valve, of reduced cross sectional area as compared with the remaining portion of the exhaust conduit. 3. An air motor according to Claim 1 in which said initial portion of the conduit is defined by a plurality of passages. 4. An air motor according to Claim 3 in which at least the portion of the conduit defining said remaining portion of the exhaust conduit is provided with a plurality of fins to assist heat exchange between the atmosphere and the wall of the conduit. 5. An air motor according to Claim 4 in which the exhaust conduits and fins are machined from solid material. 6. An air motor according to any one of the preceding claims in which said exhaust control valves are diaphragm valves. 7. An air motor according to any one of the preceding claims in which said first mentioned control valve and one of said exhaust control valves are mounted on an upper end wall of the cylinder, said cover extending downwardly around the cylinder, the exhaust conduit associated with said one exhaust control valve passing through the cover, at least said portion of the conduit being exterior of the cover.

Inventors: LUPA ZEB, LUPA, ZEB
Applicants: BINKS BULLOWS LTD, LUPA ZEB, BINKS BULLOWS LIMITED, LUPA, ZEB
Application year: 1994
Main classification: F01B31
IPC codes: F01B11, F01B31